1. Field of the Invention
The invention relates to an amplifier stage comprising first and second transistors, each having a control electrode and a first and a second main electrode, the second main electrodes of said transistors being coupled to each other via a resistive ladder having a plurality of taps a gain of said amplifier stage being switchable by selecting parts of said ladder.
2. Description of the Related Art
Such an amplifier stage is known from the European patent application EP 0 587 965 A1. A conversion of the input voltage applied across the control electrodes of the transistors is converted into a current by this resistive ladder. By bridging selected parts of said resistive ladder, a conversion impedance of the resistive ladder can be changed, thus effectively changing the gain of the amplifier stage. A disadvantage of the known amplifier stage is that the impedance of the switches, used for bridging selected parts of the ladder, becomes part of the conversion impedance seen between the second main electrodes of the transistors. As the switches are often realized as transistors, which have a non-linear impedance in a closed state, the resulting impedance between the second main electrodes will become non-linear. This will result in distortion, especially when the impedance of the closed switches is of (or close to) the order of magnitude of the resulting impedance of the ladder.